Build a Feature, Phase by Phase

One phase, one PR, reviewed and fixed in rounds before merge. A feature built in one branch can't be tried, and code merged after one review pass merges its fixes unreviewed.

main
 └─ integrate/<plan>                         cut once, before the first phase
     ├─ <plan>-phase-1 ──PR──▶ integrate     build, verify, review x2-3, fix, merge
     ├─ <plan>-phase-2 ──PR──▶ integrate
     ├─ <plan>-phase-N ──PR──▶ integrate
     └──────────────────PR──▶ main           demo, then the user merges

one phase: feat/<plan> ──PR──▶ main          no integrate branch

Start from the plan, never memory. Take the path or issue from the argument, or look under plans/ and ask if several match. Re-read it each phase. If any decision is _open_, stop and send the user back to planning. Before phase 1, check every Verify line and ## Demo: a phase with no proof and no deferral is a planning bug, cheapest to raise now.